The present invention relates generally to flammable liquid tank venting systems in general, and more particularly, is directed to a restrictive vent fitting for use with tank vapor control systems.
It is the usual practice to store flammable liquids, such as various petroleum products in storage tanks which may be either above ground or underground. In view of the fire hazard attendant with the storage of such petroleum and other hazardous products, governmental code officials, insurance underwriters and fire department officials have engaged in careful studies to establish suitable regulations to provide for the safe storage of such materials. The considerable effort and study, both in this country and abroad, with regard to suitable safety standards, has resulted in the now commonly accepted practice of storing petroleum products, such as gasoline and kerosene, in underground storage tanks of suitable size and strength for the purpose. In certain regulated instances, such as where adequate distances to populated areas can be provided, above ground storage is also permissable.
It has long been required that all petroleum products storage tanks and other flammable liquid storage tanks, either above ground or underground, be provided with suitable venting devices to equalize pressures within the tank. Most commonly, venting devices have consisted essentially of a vent pipe connected directly to the vapor section of the tank in a manner to lead flammable vapors upwardly to atmosphere at some distance above grade level. It has been found that the usual venting system as above described has generally provided adequate safety for the flammable product stored within the storage tanks and accidents directly attributable to venting have been reduced to a minimum. However, more recently, when concerned citizens became cognizant of the ecological problems arising from flammable liquid storage in relatively crowded areas, additional studies have been made of the venting systems of underground and above ground flammable liquid storage tanks. Those more recent studies were concerned primarily with the effect of the flammable vapors which were discharged into the atmosphere through the tank vents and to the environmental changes caused by the release of such vapors, rather than concern with merely the safety factors of such flammable liquid storage.
As a result of the environmental considerations, the venting systems of storage tanks are now being rapidly changed from a simple open vent to atmosphere as heretofore deemed necessary and desirable for purely safety considerations, to some type of normally closed, but openable when necessary, type of storage tank vent system, for air pollution control purposes. Traditionally, such closed and open vent systems have been installed by applying a pressure or pressure/vacuum vent fitting at the end of the tank vent line.
The pressure or pressure/vacuum vent fittings have generally proved satisfactory in reducing the discharge of flammable vapors to atmosphere. Such pressure or pressure/vacuum vent fittings normally provide either for a completely closed system under usual conditions of operation or for function of the fitting to compensate for either pressure or vacuum created within the storage tank itself. These fittings are mechanical in nature and as in any mechanical device, are subject to mechanical failure due to any one of a variety of causes. As a result of such failure, inadequate venting could result with possible dangerous consequences.